The present invention generally relates to carbon tubes, and more particularly, a method for making micrometer-sized carbon tubes.
Carbon tubes have various applications in the art. General applications of carbon tubes are found in medical research, semiconductors and microelectronics. Various methods of manufacturing carbon tubes are available in the art, including carbon arc discharge, laser ablation, condensed-phase electrolysis, and catalytic pyrolysis of hydrocarbons on various substrates such as porous anodic aluminum oxide, fine metal particles, and patterned cobalt layer.
A significant function of carbon tubes is the allowance of reactants to flow through their cavities. The inner surface of the cavities in carbon tubes can be modified by chemical treatment. The chemical treatment renders the inner surface of the cavities active with desired affinity, thereby enabling selective separation or extraction of compounds. In addition, by embedding certain transition metal complexes on the inner surface of the cavities, desired catalytic functions can be implemented.
A shortcoming of conventional methods of manufacturing small-sized carbon tubes is the inability to produce a hollow carbon tube with opening ends. This shortcoming significantly limits the capability of the carbon tube for applications that utilize the inner surface and inner space of the tubes for, e.g., selective separation or extraction of compounds, catalytic reactor or micro-reactor applications. Another shortcoming of conventional methods is the inability to produce a carbon tube with appreciable length (i.e., longer than about 1 mm), while retaining control of the tube wall thickness, the inner and outer diameters of the tubes. Yet another shortcoming of conventional methods is the inability to produce a tube with long-range three-dimensional regularity. These shortcomings have significant negative impact on practicing numerous, important applications of the carbon tubes.
Therefore, there is a need in the art for a method for making small-sized open-ended hollow carbon tubes of appreciate length with long-range regularity having effective control on the tube wall-thickness, the inner and outer tube-diameters thereof.
The present invention is related to a method for making micrometer-sized carbon tubes. More particularly, the method of the present invention comprises the steps of:
(a) coating a natural or synthetic fiber with a coating material, wherein the fiber is removable by thermal, solvent, or chemical treatment(s), or a combination thereof; and
(b) removing the fiber totally or partly, and carbonizing the coating layer and any residual fiber material.
According to a preferred embodiment of the present invention, a thermally removable polymer fiber and a material that is more thermally stable than the polymer fiber are provided. The polymer fiber is coated with the thermally stable material. The coating is carbonized and the polymer fiber is removed as a result of the carbonization process. Carbon tubes of micrometer size are then formed.